This invention relates generally to joints for orthopaedic braces and more particularly to a mechanical joint for a knee brace incorporating a locking mechanism to control and co-ordinate movement of the joint.
The human knee is not a simple hinge joint. The knee is capable of gliding, rocking and rotational movement that make it difficult to imitate in a simple mechanical joint. When the knee bends and straightens during walking or running, the femur and tibia interact in sliding, gliding and rotational movement relative to one another. It is only when the leg is straightened and supporting the weight of the body that the knee joint is locked. Thus, the natural knee joint has a point of pivot that moves about as the leg is bent and straightened with the knee providing a restricted universal action unless firmly locked as described.
When bracing the knee, it is generally desirable that the supported knee be allowed to operate in as natural a manner as possible so as not to impart abnormal forces across the joint during activity and to allow the wearer to bend and straighten the leg in a normal manner.
A leg brace requires a mechanical joint that will support the knee and reproduce as closely as possible the complex pivoting motion of the knee. At the same time, the mechanical joint must not be so heavy, bulky or complex that the normal movement of the knee is impeded. Various mechanical joints have been developed to satisfy the above requirements.
U.S. Pat. No. 3,902,482 issued Sep. 2, 1975 teaches an orthopaedic brace having a mechanical joint interconnecting brace arms that attach to the legs of the wearer above and below the knee. The joint is lightweight, relatively simple in construction and does a good job of imitating the motion of the knee. This same joint has been used in other patented braces or bracing methods such as U.S. Pat. No. 5,277,698 issued Aug. 18, 1993, U.S. Pat. No. 5,302,169 issued Apr. 12, 1994 and U.S. Pat. No. 5,562,605 issued Oct. 8, 1996. All these patents and the present invention are commonly owned.
While the mechanical joint disclosed in the above references does a good job of reproducing the natural motion of the human knee joint, the joint suffers from the drawback that it permits knee joint movement that is not natural at certain positions of the mechanical joint. For example, when the knee is straightened and locked, the lower leg should not be able to pivot. In flexion, the two halves of the joint tend to loosen relative to each other in the anterior/posterior plane which is clearly undesirable for a knee brace intended to support and guide the knee. To address this problem, the knee brace hinge was modified to include an elastic link extending between the lower arm and the joint that tends to resist movement of the lower arm when the knee is locked. This is an imperfect solution as resistance to movement of the lower arm is also present when movement of the lower arm is desired.
Accordingly, there is a need for a knee brace and mechanical joint that accurately mimics the complex movement of the human knee joint and at the same time does a complete job of bracing and supporting the knee over the full range of motion of the knee. In some positions, this involves locking one or the other of the brace arms from movement depending on the extent of flexing of the knee.
The present invention provides an orthopaedic knee brace that incorporates a locking mechanism that automatically locks one of the brace arms while unlocking the other arm to more accurately imitate the motion of the human knee and offer better bracing and support for the knee.
Therefore, the present invention provides in an orthopaedic knee brace comprising an upper arm and a lower arm securable to a wearer""s leg on opposite sides of the knee joint and a pivotable joint at the ends of the arms to allow pivoting of the knee by pivoting movement of the arms, the improvement comprising:
a locking mechanism to control pivoting of the joint to lock one of the upper or lower arms relative to the joint while automatically unlocking the other arm to permit pivoting movement of the other arm about the joint.
The brace of the present invention with its joint and locking mechanism provides a lightweight, reliable structure that is able to smoothly pivot to imitate the complex motion of the knee while fully supporting the knee.